Compression tester



Nov. 24, 1959 L. A; WOHLER 2,913,899

COMPRESSION TESTER Filed Nov. 8, 1955 2 30 I I E 5 4 i mmvrox 52 34 Y 251mm 19-12mm? United, 3 361126 Patent t This.inventiongrelatesto a device for testing. the ,com-. pression of flexible foamed material. i The, compression rrtodulus of, foamedmaterials is par-, ticularly important, in; I connection with mattresses, seat ushionsnd :thctliketbooa s he omp s o figure nd rd ndic tion; of; rmne s, and. hus f or and-also; acts as an; inde f t e ec nomy. o hemanw, f o ngtproc ss-t The foamedirubber industry; generally conform The Rubber; Manufacturers Association Inc., Buyers Specification'-Latex Feam. This specification. recites the compression test to be used in measuring cored foam materialfor compression modulus,

This test consists in measuring the loadnecessary to produce a ,25 indentation in the sample,- the test is commenced ;.by bringing a flat, circular-plate,- haying an area of 50 square inches and bearing a one pound preload, into contact with the surface .of thenfoamed member, to determine the, thickness thereof, Theimaterial is then compressed 25% of the original height at a maximum rate of 25, inches. perminutetby ncre e loading ontthe'plate, andthe final total load,- is :observedapproximately..5 secondsafter.thepla eh sc me o res Th total weight is recorded as the R.M.A. compression value.

Heretofore, reliablelccompression measurements of such items as full-,size mattresses andsin ilar objects, of large area couldbe made only with expensive factory equipment designed to reach inwardly over the mattress from the outside edges. In addition to the expense of present factory measuring equipment, further disadvantages are inherent in the space necessary to accommodate largescale caliper-type equipment and the attendant geartrains, springs and the like.

At times it becomes necessary to check the compression modulus under conditions of depressed temperatures; much-presently known equipment for cold-testing becomes difiicult to operate and the transmission of data to stations outside the test chamber unreliable and involved due to the low temperatures.

The present invention overcomes the disadvantages of the prior art by providing an inexpensive, portable device for very accurately measuring the physical characteristics of resilient material.

It is, therefore, the object of this invention to provide means for quickly and accurately measuring the thickness and the compression modulus of resilient material.

It is a further object of this invention to provide a portable device for measuring very accurately the compression modulus and thickness of foamed mattresses and other cored cushioning materials.

Another object of the invention is the provision of a lightweight compression tester for flexible, foamed, cored material.

Still another object of the invention is to provide an inexpensive compression tester for large flexible foamed objects which is substantially unaffected by extremes in temperature.

Further details of the device of the invention will be apparent from reference-to the following description,

drawings and claims of a preferred form of the inventoin, in which:

Figure l ista side elevatiompartlyin'section, showing, the device, of the invention assembled. and.in unloaded position ona section ofcored,-foamed material;

Figure 2 is:;a-view: similar to Figure 1, ,showing the weightsinzplacet.

Figure 3;.is, a sectional view of the, device of the inventiongtaken substantially-along.line 3-3 of Figure 2; and.

FigureA is -.a:top plan view of thedevice.

Referring now particularly to. Figure 1 of the drawings, the tester, indicated generally at 10 is shown in connection with ,a piece... of foamed. material .11, whosev compressiommodulus is tobe determined. The tester comprises:two cooperating-portions, a foot 12 and an indicator13; The foot 12 comprises a- 50 square inch circular'plate 14having a shoulderportion 15 and a centeropenin g; 16 threaded as at-17, and a tubular member 18 having a reduced tapered portion 19 which is threaded'at 20'to engage threaded portion H at the plate 14.v The upper portion of the tubular member 18 is provided with a'n;axial slot 22' having a width preferably smaller thangthfe inside-diameter 23 of the tube.

The end; of the upper portion of member 18 is beveled, 1 asgat 24.5

The foot 12 isidesignedlto weigh exactly one pound, to ,give theone: pound preload required" by the R.M.A. procedure. 7

i The indicator comprises, a cylindrical spindle 26 adapted to beslidably supported .within the tubular member'18fand carries atone enditwo scales 27 and'28 withinja frame 29.,

Preparatory to theuse of the compression tester, a small slit is made through the foamedmaterial 11 over one. of thejcore-holes 3 2, asat 30. The taperedportion 19:05 the foot is insertedfully into the foam material at the cm. and the lower end' of the spindle 26 of" the indicator brought to rest'on thesame surface 34as the foam ma t 'Thedistance between the lower endof'the spindle 26 and the bottom of the plate 14 is 6 inches, as indicated on scale 27, on which the digits are 1 inch apart. Thus, the actual thickness of the foam material is shown on scale 27 of Figure 1. Circular weights, such as 35, though heavier ones of which are provided with flanges 36 for easier handling, are stacked onto the plate 14 concentrically with the tubular member 18 compressing the foam material. The digits on scale 28 are spaced inch apart and this scale is so placed in relation to scale 27 that a reading on scale 28 equal to the original reading on scale 27 indicates a 25% displacement. With a reading on scale 28 of 6 inches, as shown in Figure 2, the foam material has been compressed 25%. The total of the weights 35 and the one pound preload corresponds to the R.M.A. compression.

The slit 30 made through the top of the foam material is so small as to be practically invisible after removal of the tester, and the slit in no way detracts from the quality of the material. If desired, it may, of course, be cemented shut.

From time to time, the R.M.A. circulates among the participating manufacturers representative samples of foamed material to be tested on factory equipment, in accordance with the R.M.A. standard test. Some of the samples submitted were likewise checked for compression with the device of the present invention, as well as with extremely accurate and sensitive laboratory equipment. Summarized below are the resulting compression data illustrating the high degree of accuracy of the device of the invention.

Ica Baten ed Nov, 24,1 5

Portable tester of the invention, lbs.

Average from 9 factory testers, 6

different mfrs.. lbs.

Laboratory Sample tester, lbs.

Pillow half Cored bulk stock Mattress Furtherdata illustrating the accuracy of the portable device of the invention, both in measuring thickness and compression, are shown below, where nine AVz-inch mattress sections were tested and the results compared with those obtained using laboratory equipment. Two non-consecutive blind tests were made on each sample, with the following results:

Height Measure- RMA Compression,

d ment.lnches Labora- Y Tester Portable Tester Laboratory Tester Average.--"

described, it is to be understood that differ'ent types of indicators may be used, as well as a different-size foot, and difierent weights, in conjunction with conversion factors, without departing from the spirit and scope of the present invention, the essential features of which are summarized in the appended claims.

I claim:

1. A device for measuring the; compression characteristics of a slab of compressible material of substantial size and thickness as it rests on a supporting surface, said slab having a perforation extending completely through its thick dimension, said device comprising a rod of substantial length adaptedto extend through said perforation to rest on said surface and having an upper portion extending upwardly beyond said slab for a substantial distance, and a graduated scale affixed to said upper portion, a fiat plate of substantial area having a hub freely slidable longitudinally of said rod and comprising a portion extending completely-through said perforation, said plate being supported by the portion of material adjacent said perforation, means exerting a force on said plate to compress said material a predetermined amount, said plate taking a position relative said rod as determined by the compression strength of said supporting material and the magnitude of said force, and means connected to said plate indicating on said scale the relative position of said plate'on said rod.

2. The device of claim 1, in which said slab is of cored stock, and in which said perforation communicates with one of said cores.

3. The device of claim 1, in which said means exert ing force on said plate comprises weights.

4. The device of claim 1, in which said means, comprises annular weights concentric with said rod.

References Cited in the file of this patent UNITED STATES PATENTS 

